Estrogen predicts breast cancer recurrence: study

By Julie Steenhuysen

CHICAGO (Reuters) - Blood taken from women whose breast cancer returned showed high levels of estrogen even though many had been treated with estrogen-blocking drugs, U.S. researchers said on Thursday.

They said the finding suggests women who have had breast cancer should take extra steps -- such as regular exercise and weight management -- to reduce their estrogen levels and minimize the risk that their cancer will return.

Estrogen is strongly linked with the initial development of many breast cancers, but few studies have looked at the link between high estrogen levels and cancer recurrence, especially in women who are taking anti-estrogen drugs like tamoxifen.

"This is the largest study to date and the only one to have included women taking agents such as tamoxifen to reduce estrogen's effect on cancer growth," said Cheryl Rock, a professor of preventive medicine at the University of California, San Diego, whose study appears in the journal Cancer Epidemiology, Biomarkers and Prevention.

Rock said taking anti-estrogen drugs like tamoxifen may not completely wipe out the hormone's effect in women who have high levels of estrogen. Tamoxifen transformed breast cancer therapy when it was shown to reduce the risk of cancer coming back by close to 50 percent.

But Rock said women on that pill or a newer class of drugs called aromatase inhibitors should also consider some basic preventive measures.

"You can't just assume because you've got one drug that has good effect that you should forget about all of the other useful things that you might be able to do," she said in a telephone interview.

Rock and colleagues drew their conclusions from a dietary intervention trial that followed 3,088 women who had been treated for early stage breast cancer but who were cancer-free at the time they enrolled.

They identified 153 women from the study whose cancer had returned and matched them with 153 who were cancer-free after seven years. The women were matched up by type, body size, age, ethnicity and use of chemotherapy and other items.

CONNECTING THE DOTS

About two-thirds of the women had been taking tamoxifen, and 78 percent of them had so-called estrogen-receptor positive cancers -- tumors that need estrogen to grow.

When they looked at blood samples taken at the start of the trial, the researchers found women whose cancer came back had more than the double the concentration of estrogen compared with women who remained cancer-free.

"For us it just connects the dots from what we would expect and now we will go forward and find lifestyle modification factors that would be a benefit for this target group," Rock said.

She said moderate to vigorous exercise has been shown to help lower estrogen in the general population. "There is no reason it wouldn't in a breast cancer survivor," she said.

And she said weight management would be especially useful to these women. Studies have found that women who put on a lot of weight at any stage of adulthood increase their risk of breast cancer, likely because estrogen accumulates in the fat and promotes tumors.